This invention relates to generator stators and, more specifically, to a wedge and slide system that can be used internally of the end wedge and permits in situ radial correction for radial pressure and dimension losses which occur over time.
Electric utility companies require large turbine-generators to operate reliably for long periods of time, for example, thirty years or more. Normal, steady-state electromagnetic forces acting on the armature winding are capable of causing armature bar vibration within a much shorter period than the expected generator lifetime. Armature bar vibration can occur if radial clearances are present within the stator core slot. Bar vibration can result in armature bar insulation abrasion. The abrasion can become severe if maintenance actions are not taken to retighten the slot support system and arrest the vibration. Typically, a prolonged maintenance outage is required to retighten the slot support system and eliminate radial clearances within the slot.
The electrical windings within the ends of the stator core slots may become susceptible to accelerated abrasion due to: 1) pre-existing or rapidly-evolving radial clearances, 2) the effects of excessive or continuous oil contamination, and 3) abnormally high electromagnetic design forces on the slot portion of the winding. It is therefore important to provide an in situ means for eliminating radial clearances that develop in this location in order to prevent unscheduled or prolonged service outages.
In an attempt to address at least some of these problems, a stepped wedge and slide arrangement is proposed in U.S. Pat. No. 4,149,101 but for the purpose of preventing axial displacement of wedges within the core slot. A stepped bracing arrangement is proposed in U.S. Pat. No. 3,842,303 but in the context of an end winding support fit-up device between the coil end arms.
A stepped dovetail wedge and slide system which permits retightening of the generator stator end slot wedges so as- to restore the required radial force on the winding bars is disclosed in copending application Ser. No. 09/453,776 filed Nov. 22, 1999, now U.S. Pat. No. 6,294,855 and entitled "Adjustable Generator Stator Slot Wedge System").